In their most basic foil, vacuum lifters incorporate a system that includes a vacuum supply, some means of controlling when the vacuum is applied, and one or more vacuum pads or seals that interface with the surface to which it is being attached. By drawing air from between the vacuum pads and the interfacing material, vacuum is generated. This vacuum is a pressure differential between the local atmospheric pressure and the pressure between the vacuum pads and the attachment surface. The net result is a force that draws the vacuum pads and the surface together. This force allows for the material to be lifted or manipulated by means of the machine or similarly can be used to mount a device to a surface.
One of the key factors to the operational safety of vacuum lifting equipment is ensuring that a minimum vacuum level is maintained between the vacuum pads and surface. Many regional standards also extend this requirement to non-typical conditions, such as when system power is interrupted. The required minimum vacuum level depends on many factors including the number of vacuum pads, the size of the vacuum pads, the rigidity of the lift machine and of the material to which the lift machine is attached, the arrangement of the vacuum pads, the style of the vacuum pad seals, and the surface characteristics of the material. Additionally, the coefficient of friction between the vacuum pads and the material is an important factor.
Vacuum lifters commonly incorporate a basic means for controlling the supply of vacuum and providing indicators of the vacuum level. These functions are typically managed through the use of one or more vacuum switches set at predefined levels. When the preset levels are achieved either on a rising or falling vacuum progression, indicators and vacuum supply can change state.
More particularly, a vacuum attachment device consists of one or more vacuum circuits, wherein each circuit consists of several components connected using manifolds, hoses and/or fittings. Those components conventionally include (i) one or more vacuum pads each with a sealing edge and a face which resists sliding when pressed against a surface using the force generated by vacuum, (ii) a vacuum source such as a vacuum pump or venturi which can be used to evacuate the air from a vacuum circuit, (iii) a controller with two or more states, the first state being using to attach the vacuum attachment device to a surface by causing the vacuum source to be applied to the vacuum pad, and a second state used for detaching or releasing from said surface, in which state the vacuum source does not draw air from beneath the vacuum pads, and (iv) a control interface for the operator to select between the states of the controller so as to control whether the vacuum attachment device attaches to said surface or is released from it. This control interface may be a knob or lever which operates a controller implemented as a valve, switches or buttons for providing control signals to an electrical or electronic controller, or another type of interface with similar function.
Representative examples of vacuum attachment devices, and in particular vacuum lift equipment, are sold by Woods Powr-Grip Co., Inc., such as Wood's Powr-Grip Co., Inc.'s Channel Lifter and Manual Rotator 2800. A variety of instruction sheets for such devices and vacuum cups, identified as Operating Instructions for MODEL NUMBERS: P11004DC2, P1HV1104DC2, P11104DC2, SINGLE-CHANNEL LIFTER, DC-VOLTAGE WITH DUAL VACUUM SYSTEM (AVAILABLE WITH REMOTE CONTROL SYSTEM) and INSTRUCTIONS International Version MODEL NUMBER: MR1611LDC, MANUAL ROTATOR 2800 DC-VOLTAGE, are appended hereto and are hereby incorporated by reference into this disclosure as though all subject matter of such documents is expressly herein presented.
Vacuum attachment devices of this type are used in both stationary and lifting applications. Stationary applications include holding a device to a surface as an anchor point such as for a fall restraint system. Lifting applications include those in which a vacuum attachment device is mounted to a frame. The device is attached to a workpiece (such as a piece of glass, stone or metal), then the frame can be lifted in order to also lift and manipulate the workpiece.
Traditional control systems on below-the-hook vacuum lifters, such as those commonly used to lift sheet materials like glass, stone, metal, insulated panels, fiberglass, etc., are limited in their ability to manage and control nuances in the system response. It is the operator's responsibility to not only manage the process of attaching, lifting, positioning, and ensuring the load is securely placed before releasing, but also to monitor system functions, perceive changes in the function, regularly check indicators, and correlate these with their associated risks. In prior implementations, vacuum switches were used which switch from a first state to a second state at one vacuum level and back to the first state at a different vacuum level (i.e., they have a threshold level and utilize hysteresis). They are unable to distinguish between a large number of vacuum levels.
Accordingly, a need exists for vacuum-based handling equipment and controls that improve safety and enable an operator to better focus on their primary purpose in moving material. The present invention addresses this and other needs.